For decades, Codelco's underground mines have successfully used the block and panel caving method, achieving high yield rates and competitive costs. At the beginning of the 20th century, the deposits the corporation exploited were on secondary rock, which has a medium to intense degree of fracturing, offering a highly favorable environment to apply the blasting system. For some years now, this type of mining has been facing ever more demanding and difficult scenarios, having to adapt to deeper deposits, with more competent rock masses and environments that require greater efforts.
The underground exploitation of higher competence unprocessed ore through block caving has meant an important increase in the material's granulometry, which is generated as a result of the natural breakup of the rock mass. This situation has caused the mineral extraction operation to be faced with frequent interruptions due to the presence of large masses in the extraction point (trenches), which are present as boulders or oversize muck on the floor or as overhangs. One of the most complex and riskier interferences to solve is caused by the blockage of these boulders inside the trench (trench overhang) at heights that vary between 4 and 12 meters.
The problem of trench overhangs, typical in block caving operations, has been faced using high risk procedures. The commonly used solution consists in placing explosives with bamboo tamping. Usually, this operation consists of placing pentolite cones tied to the end of the bamboo sticks, which lift it, put it in contact with the rock and hold it until the loosening blast is done. This practice requires that the operator in charge of placing the explosives approaches the mouth of the area, in order to see the position where the explosive will be located and to place it in height, an action that leaves them greatly exposed and vulnerable to risk, in case a sudden mineral flow occurred.
An important progress for the underground mining industry has been achieved with the development and implementation of a semi-automated and self transportable handling arm to release overhangs, which was presented in our Chilean patent application number 1970-2014, and its content forms part of the present application.
In the state-of-the-art there are no mechanical devices adapted to carry, handle and place an explosive cone, when releasing overhangs in underground mines; though there are some devices to carry and/or fix explosives, none of them has the characteristic of carrying an explosive cone that can also be remotely operated and that has the capacity to fix the explosive cone on an overhang. In this way we have, for example, the U.S. Pat. No. 2,837,997, which describes a device used in seismic explorations where an amount of vertically separated explosives are lowered through an impact hole and blasted inside said hole. Said device consists of a long cylindrical container which is filled with explosives; on the external area of the container, there are split rings used to fix the external wall of the container to an end of it. The U.S. Pat. No. 4,089,250 describes a support to hold an explosive cartridge in a chamber that consists of: a cylinder that is substantially closed on one end and open on the other, designed to be received into the chamber. Said cylinder has a bigger inside diameter on the open end and gas exhaust ports near to the closed end; a reel of such a size that allows adapting it inside the cylinder; indication means and indicator joined to the observable reel on the closed end of the cylinder; spring means to push the reel towards the open end of the cylinder and force the support's cartridge support. In our Chilean invention patent application 1117-2010, a mobile system to place elements at a height, preferably inside an underground mine, is described; this system includes an object-carrying system, which is individualized as an explosive carrier system, but there are no extensive specifications of the system itself. In our Chilean invention patent application 1970-2014, a semi-automated, self-transportable and remotely operated handling arm is described, for the mapping and release of overhangs in extraction points of underground mines. In said request, a cone-carrier system is also mentioned; however, no further information is provided about said cone-carrying device.
As it can be seen, there are no mechanical devices in the state-of-the-art for the carrying, handling and placement of an explosive cone to release overhangs in underground mines.